<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>子元素选择器示例</title>
    <link href="../css/_7.css" type="text/css" rel="stylesheet">
</head>
<body>

    <div id="top">网页顶部</div>

    <div id="nav">
        <ul>
            <li>菜单 1</li>
            <li>
                菜单 2
                <ul>
                    <li>菜单 2 的子菜单</li>
                </ul>
            </li>
        </ul>
    </div>

</body>
</html>